The invention relates to bar product, cylinder rods, hydraulic cylinders, and methods for manufacturing bar product, cylinder rods, and hydraulic piston cylinders. More particularly, the invention relates to bar product prepared from microalloyed bar steel and which can be formed into cylinder rods for use in hydraulic cylinders. The bar product and cylinder rods can be prepared without a step of cold drawing.
Manufacturers of hydraulic cylinders often require cylinder rods that satisfy the chemical and property requirements of ASTM A 311. Bar steel used in the manufacture of hydraulic cylinders is conventionally heavy-draft cold-drawn and stress-relieved and satisfies the chemical and property requirements of ASTM A 311-Class B.
Cylinder rods can be produced from bar steel and processed according to ASTM A 311. Bar steel characterized as grade C1045 or grade C1050 according to ASTM A 311 is melted and cast into a preform. The preform can typically be considered a billet, bloom, or ingot. The preform is reheated to a working temperature of about 2,000xc2x0 F., and is hot rolled on a multiple stand bar rolling mill to provide a desired round size steel bar. The steel bar is cooled to below 1,000xc2x0 F. on a notch-bar cooling bed. The cooled bar can be referred to as xe2x80x9cas-hot rolled bar.xe2x80x9d The as-hot rolled bar is typically shipped to a cold finished bar producer for further processing. The mill scale is typically removed by shot blasting. The as-hot rolled bar is cold drawn to a smaller cross section by pulling it through a lubricated die. The standard draft for the cold finished bar industry is {fraction (1/16)} inch. A heavy draft is typically xe2x85x9 inch to {fraction (3/32)} inch depending on the desired properties and finished cold drawn size. The reduction provided by a heavy draft results in additional strength. The cold drawn bars are straightened, and given a stress relief heat treatment to relieve drawing stress and increase the yield strength. The stress relief heat treatment is typically provided at about 500xc2x0 F. to about 700xc2x0 F. The resulting bars are typically processed by any or all of the following processing steps including turning, grinding, polishing, surface hardening and chrome plating to achieve a precision size and surface finish.
Microalloyed steel generally contains of one or more of columbium (niobium), vanadium, titanium, and nitrogen. These elements can be added to a base steel composition such as grade C1045 or grade C1050, and strength can be increased by a combination of grain refinement and precipitation strengthening. Because the microstructure of the steel remains predominantly pearlitic at the carbon levels provided by grade C1045 and grade C1050, ductility at a given strength level is relatively low, and tends to decrease proportionately as tensile strength increases. Yield strengths above 100 ksi can be achieved for microalloyed steel, but the ductility may not meet the requirements of ASTM A 311, Table 2. Steel companies have improved ductility in high strength microalloyed steel by lowering the amount of carbon and compensating for the resulting strength decrease by adding manganese and other elements. Hydraulic cylinder rod producers, however, have been reluctant to accept cylinder bars which are not certified as meeting the requirements of grade C1045 and C1050 according to ASTM A 311. One concern is that lower carbon steel will not respond to the induction hardening commonly performed to improve wear at the rod surface.
A bar product prepared from microalloyed bar steel is provided according to the invention. The bar product is prepared by hot rolling and heat treating a microalloyed bar steel. The hot rolled and heat treated microalloyed bar steel is prepared by steps of hot rolling a preform of the microalloyed bar steel at a temperature of between about 1,400xc2x0 F. and about 2,300xc2x0 F. to provide a steel bar having a diameter of between about xc2xe inch and about four inches, cooling the steel bar to provide a surface temperature of below about 1,100xc2x0 F., and heat treating the steel bar in an environment having a temperature of between about 500xc2x0 F. and about 1,300xc2x0 F. The bar product is preferably prepared without a step of cold drawing. In particular, the bar product is preferably prepared without a step of drawing to provide a 10% to a 35% reduction.
The bar product having a diameter of between about xc2xe inch and about four inches can be characterized as having a tensile strength of greater than about 105 ksi, a yield strength of greater than about 90 ksi, an elongation in two inches of greater than about 7%, and a reduction of area of greater than about 20%.
The microalloyed bar steel preferably includes about 0.36 wt. % to about 0.55 wt. % carbon, about 0.60 wt. % to about 1.65 wt. % manganese, 0 to about 0.050 wt. % phosphorus, 0 to about 0.050 wt. % sulfur, 0 to about 0.40 wt. % silicon, 0 to about 0.06 wt. % tin, 0 to about 0.40 wt. % copper, about 0.01 wt. % to about 0.40 wt. % nickel, about 0.01 wt. % to about 0.30 wt. % chromium, about 0.01 wt. % to about 0.15 wt. % molybdenum, and about 0.005 wt. % to about 0.50 wt. % microalloying additive comprising at least one of columbium (niobium), vanadium, titanium, aluminum and nitrogen. Preferably, the microalloyed bar steel includes about 0.02 wt. % to about 0.40 wt. % vanadium and between about 0.005 and about 0.025 wt. % nitrogen. More preferably, the microalloyed bar steel includes between about 0.005 wt. % and about 0.10 wt. % columbium (niobium), between about 0.02 and about 0.40 wt. % vanadium, and between about 0.005 wt. % and about 0.025 wt. % nitrogen. The microalloyed bar steel can additionally include between about 0.005 wt. % and about 0.05 wt. % titanium and between about 0.020 wt. % and about 0.060 wt. % aluminum. The microalloyed bar steel preferably includes between about 95.5 wt. % and about 99.0 wt. % iron.
The bar product can be further processed to provide a cylinder rod according to the invention. Exemplary processing steps can include turning, grinding, and/or polishing to provide a precision size. In addition, the surface of the bar product can be surface hardened and/or chrome plated.
A method for manufacturing bar product is provided according to the invention. The method includes steps of hot rolling the microalloyed bar steel at a temperature of between about 1,400xc2x0 F. and about 2,300xc2x0 F. to provide a steel bar having a diameter of between about xc2xe inch and about four inches, cooling the bar steel to provide a surface temperature below about 1,100xc2x0 F., and heat treating the steel bar at a temperature of between about 500xc2x0 F. and about 1,300xc2x0 F. The bar product can be further processed by steps of turning, grinding, and/or polishing to provide a precision size, and the surface of the bar product can be surface hardened and chrome plated. The method can be used to provide a cylinder rod for as a piston in a hydraulic cylinder.
A hydraulic cylinder is provided according to the invention. The hydraulic cylinder includes a housing and a cylinder rod provided within the housing. The housing includes an opening through which the cylinder rod extends. The cylinder rod includes a first end and a second end. The first end extends out of the housing through the housing opening and is generally attached to a saddle which is then attached to a substrate. The second end generally remains within the housing. The housing additionally contains a surface for mounting to another substrate.